The present invention relates to all golf clubheads, but more particularly irons and putters, where consistent distance and direction are more desirable than the maximum distance usually sought with low lofted woods and metalwoods. The present invention relates specifically to improved clubhead and clubhead insert designs, which substantially reduce or totally eliminate mishit distance loss.
Golf shots lose both distance and directional accuracy when a golf ball is struck at a clubface location not aligned with (i.e. directly in front of) the clubhead center of gravity. Misdirection is primarily caused by the angular rotation of the clubhead upon impact with a ball not aligned with the xe2x80x9cclubhead center of gravityxe2x80x9d (which includes the effect of clubshaft weight). Mishit distance loss is caused by both the misdirection [one minus the cosign of angular difference between initial line and post impact deflected line] and clubhead energy lost to clubhead rotation rather than transferred to the ball at impact.
These effects have long been postulated and intuitively observed by skilled golfers and club designers. Only in the past decade, however, have these effects been quantitively and empirically measured using ball striking robots featured in club and ball test reports in popular golf literature. Irons and woods (including metalwoods) have been tested with the famous xe2x80x9cIron Byronxe2x80x9d and similar robots. Putter tests using Dave Pelz""s xe2x80x9cPerfy(trademark)xe2x80x9d were periodically published in Golf Magazine (i.e. July 1994 pg. 64-65; March 1995).
Pelz putter test percent distance losses for xe2x85x9cxe2x80x3 and xc2xexe2x80x3 mishits are summarized below:
The above published Pelz data indicates that putterheads with the highest moment of inertia around the center of gravity tended to have the lowest percent distance loss. Doubling the mishit distance (i.e. from xe2x85x9c in. to xc2xe in.) tripled the distance loss.
In the art, Beaumont (U.S. Pat. No. 5,529,543) and Rohrer (U.S. Pat. No. 5,766,093), the disclosures of which are both incorporated herein by reference, both claim clubhead insert devices reducing mishit distance loss via variable energy absorption (more at center than periphery). Beaumont claims improved irons using a single energy absorbing xe2x80x9ccomponentxe2x80x9d or xe2x80x9cplugxe2x80x9d of variable thickness (thickest at club center). In some claims, the single energy absorbing plug is behind a rigidly attached thin plate of stiff or hard, but flexible, material.
Softer elastomeric striking faces are less desirable than harder polymer or metal faces for both putters and irons for durability, feel, and acoustic reasons. Beaumont anticipates some of the above limitations in his claims 9-19 by rigidly affixing xe2x80x9cby epoxy or the likexe2x80x9d to the rigid clubhead body, a xe2x80x9cthin plate . . . which is stiff, or hard, but deformable upon impact . . . xe2x80x9d over the energy absorbing void or elastomer.
Rohrer uses a plurality of energy absorbing elastomer xe2x80x9celementsxe2x80x9d, plugs, or components with or without faceplates with the deadest elements at the center of the clubhead and elements of more lively material more remote to reduce or eliminate mishit distance loss on putters.
Others have used either a single uniform thickness insert on putters to influence total distance (increase or decrease) and for feel (vibration feedback), but not to reduce mishit distance loss. Still, others have used multiple hardness materials to influence mishit ball direction or feel, but not to reduce mishit distance loss.
The subject invention provides alternative means to correct for mishit distance loss in putters and irons using more durable, compact, and practical variable energy absorbing designs than the prior art. The undesirable xe2x80x9ctrampoline or spring facexe2x80x9d and xe2x80x9cincompressibilityxe2x80x9d effects of the prior art are overcome.
It is important to recognize that an elastomer""s (or any other solid material) hardness (as typically characterized as Durometer or Elastic Modulus) is totally distinct from, and unrelated to, its energy absorbing properties (typically characterized as Bayshore Rebound % or Coefficient of Restitution). Some hard elastomers (like a squash ball) can be very dead while much softer elastomers (like multi-colored urethane xe2x80x9csuperbouncexe2x80x9d toy balls) can be extremely lively.
Putter tests conducted by Rohrer using an impact robot (xe2x80x9cStainless Stevexe2x80x9d who produces repeatable identical velocity strokes) on the constructions taught and claimed in Beaumont Claims 9-19, show that when thin metal or rigid plastic flexible faceplates or coverplates are rigidly attached to part or all of a clubhead periphery, most or all of the effect of any underlying variable energy absorbing mishit distance correcting mechanisms are lost for the following reasons:
1. To be durable and practical, Beaumont""s thin cover plates must be metallic or have comparable stiffness and durability properties. When a metal cover plate is xe2x80x9crigidly attachedxe2x80x9d or affixed around all or part of its periphery to a rigid clubhead body (defined herein as, that when there is little or no relative movement between the coverplate and clubhead body at the attachment points), then the coverplate produces a xe2x80x9ctrampoline or spring face effectxe2x80x9d which may actually absorb less energy than a solid clubhead with on-center hits (Reference 11-98, Golf Smith Magazine, pgs. I-1, I-2, I-7 and I-8). If an energy absorbing (low rebound rate or viscoelastic) elastomer is placed behind a xe2x80x9cstiff hardxe2x80x9d rigidly affixed flexible faceplate of practical thickness, the impact with a golf ball will not produce sufficient faceplate and underlying elastomer deflection to absorb the clubhead kinetic energy required to correct for a typical mishit. For purposes herein, a flexible faceplate is defined as a cover layer of a material of equal or greater hardness than a golf ball or ball cover and of sufficient durability for practical multiple ball strikes which cover layer would deflect, but not permanently yield or deform, upon typical impact velocity of play if said cover layer were not partially or fully attached or constrained around its periphery.
2. An energy absorbing, low rebound rate, viscoelastic elastomer constrained in a cavity behind any thin and stiff, or hard faceplate, can only absorb energy if it is sufficiently deformed. Elastomers behave like incompressible fluids. Even if the rigidly affixed faceplate overcame the trampoline effect limitations described above, the elastomer""s fluid-like incompressibility would require that the faceplate deflect outward at locations remote from the ball impact point to provide sufficient viscoelastic deformation for adequate energy absorption. We shall hereinafter refer to this as the elastomer xe2x80x9cincompressibility effect.xe2x80x9d To illustrate the above effects, clubheads according to FIGS. 1 through 4 were constructed and tested using an impact robot, xe2x80x9cStainless Stevexe2x80x9d, which reproduces identical clubhead velocity throughout the tests. FIG. 1 (A and B view) was a solid aluminum putterhead. FIGS. 2 (A and B view) and 4 used a xe2x85x9c in. deep high energy absorption ( less than 10% Bayshore Rebound) elastomer of approximately 70 Durometer A hardness embedded (cast) into an aluminum clubhead cavity. In FIG. 4, a thin, hard (stainless steel) coverplate in intimate contact with (bonded to) the elastomer was rigidly attached (epoxied) to the clubhead body (a softer acetel plastic coverplate was similarly attached and tested). In FIG. 3, the same two coverplates (0.060 in. acetel and 0.060 stainless steel) were again epoxied to the clubhead with the viscoelastic inserts removed.
The FIG. 2 insert showed a 30% distance loss (versus the FIG. 1 solid aluminum clubhead) when struck before the clubhead center of gravity and 50% loss with xc2x1xc2xe in. mishits (laterally). FIG. 3 showed no distance loss versus FIG. 1 with either the stainless steel or acetel cover plates illustrating the xe2x80x9ctrampoline effectxe2x80x9d discussed above. FIG. 4 showed no distance loss with the stainless cover plate (due to both the trampoline and incompressibility effects previously discussed). With the acetel cover plate, FIG. 4 distance loss was reduced to about half the FIG. 1 values. Thus, even with a relatively elastic acetel faceplate, not durable enough for practical iron play, and a very deep (0.375 in.) insert of extremely dead material ( less than 10% Bayshore Rebound) we could only get about half of the center of clubface energy absorption required for full mishit distance correction.
It is highly desirable in clubhead design to make mishit distance correctly energy absorbing inserts for both irons and putters as thin or compact, and therefore efficient, as possible thus, allowing them to be incorporated into existing popular clubhead designs without making such clubheads appear fat or bulky. The subject invention allows greater clubface deflection and thus, greater elastomer deformation and energy absorption thus, allowing energy absorbing inserts to be more efficient and compact.